This invention relates to seals and, more particularly, to seal constructions adapted for use between a movable piston rod and a stationary housing to prevent the escape of compressed fluid along the piston rod.
Pneumatic springs are well known that contain gas such as air or nitrogen under high pressure in the cylinder cavity. In an attempt to prevent escape of gas from the cylinder cavity along the piston rod, a chamber containing a liquid such as oil has been provided adjacent the apertured end wall through which the piston rod reciprocates.
Such pneumatic springs may be used in resilient support columns such as disclosed in U.S. Pat. No. 3,856,287. They may also be used for biasing the tail gate of a station wagon in the open position as disclosed in U.S. Pat. No. 4,263,488 and the prior art disclosed therein. In addition, these springs may be used in pneumatic suspensions, such as disclosed in U.S. Pat. No. 4,030,716.
These springs with a liquid chamber adjacent the apertured end wall provide an excellent seal for the compressed gas. Even so, gas eventually works past the fixed seal between the liquid and gas chambers because of the pressure differential across this seal. The resulting accumulation of gas in the "liquid" chamber works past the seal at the apertured end wall much faster than does the liquid. Also, the higher concentration of gas in the "liquid" chamber results in less lubrication of the endwall seal by the liquid, and some sensitivity to the orientation of the gas spring in a particular installation. In addition, the load on the seal between the liquid and gas chambers due to the pressure differential causes friction and wear on this seal.